Process for the removal of cyanogen compounds from gases



f TE ST TE H J I :1,924,2 os

" v I rnoorfss. ron: THE RnMovAn. F

, q 1 n can oo vrro Nps FROM GASES Christian-Johannes Hansen, Essen-Ruhr, Ger- 1 many, assignor, by. mesne assignments,,to The -Koppers Company of Delaware, Plttsburgh,

crimp; t

- Pa., a Corporation of Delaware No Drawingf' Application January "2s,"--19a1," 1

Thisi ention relats 'to'a process for the removal ofcyanogen compounds from gases.

The removal of cyanogen compounds from gases such as coal distillation gases by scrubbing with ammonium polysulphide liquors with the 'formation of ammonium thiocyanate has been proposed hitherto. In carrying out this process in the manner hitherto known considerable difficulty has been encountered owing to the fact that the absorption of the cyanogen compounds is in the gas industry, the removal of cyanogen compounds does not present any particular difficulty. In such cases a mere washing of the ammonia-containing gas with an aqueous sus-' ,gq; pension of sulphur is sufilcient.

" If, however, the temperature of the gas and consequently also that of the wash liquor rises for whatever reason above the value given above, which may, of course, happen as a result of a breakdown in the cooling water installation, or when a part of the cooling installation is shut off for repair, then the washing out of the cyanogen compounds becomes very incomplete. For example, at a temperatureof 50 C. to 60 C. it has 3Q? not been possible hitherto to remove more than to of cyanogen compounds from gases with a normal content of one gramme of cyanogen compounds per cbm. calculated as HCN.

Apart from the loss in cyanogen nitrogen the 5 dropping ofi in the efiiciency of the cyanogen washing is particularly disturbing if the gas is to be given a further treatment for the removal of ammonia and sulphuretted hydrogen, for 'example, with alkaline iron thionate liquors which 3 0;: may also contain suspended iron hydroxide. In

the latter case the cyanogen compounds and the iron salts form insoluble iron-cyanogen residues which may interfere seriously with the later operation of the washing process by stopping up the I; apparatus, and also with the working up of the spent wash liquors to pure ammonium sulphate.

and sulphur.

The surprising observation has now been made that cyanogen compounds can be removed completely from gases even when the temperature of If {clai s-f (01. 234

" sesame. 510,846, and in Germany January 25,

the said gases in the wash liquo r rises "above30 C. for example to C. to C. so long as the wash liquor contains polysulphides in the form of higher polysulphides than the bisulphide.

Accordingly, the present invention comprises a process for the removal of cyanogen compounds from gases .by bringing the latter into contact with an alkali polysulphide (for example ammonium polysulphide) liquor which process is characterized 'by employing a liquor containing polysulphides higher than the bisulphide and maintaining a suificient excess of the said higher polysulphides in the liquor throughout the washing process to preventthe formation of mono sulphides.

The presence of sufiicient excess of higher polysulphides in the liquor is maintained according to the invention by adding to. the liquor before or during the washing process at least I one equivalent of sulphur andone equivalent 7 of ammonia for each cyanogen group in the gas in the form of dicyanogen-or 'hydrocyanic acid.

The characteristic effect obtained in the process according to the invention may possibly be explained on the assumption that sulphur can be added to bisulphide and higher polysulphides sufiiciently rapidly at temperatures above 30 C. for example at 60 C. to 70 C. so that the higher polysulphides required for the combination with the cyanogen compounds, according to the following equations, can be regenerated directly by. elementary sulphur Against this the ammonium sulphide produced from ammonium disulphide, for example, accord ing to the equation:-

not merely become slightly milky but should immediately give an opaque suspension of precipitated sulphur.

pounds from gases comprising bringing gases at I atemperature above 30 C. and containing cyanogen compounds into contact with an ammonium polysulphide liquor containing ammonium polysulphides higher than bisulphides to remove the cyanogen compounds from said gases and maintaining a' sufficient excess of the said '7 higher polysulphides in the liquor throughout the washing process to prevent the formation of ammonium monosulphides; excess of higher polysulphides being maintained in the liquor by adding thereto before the washing process a quantity of sulphur and ammonia not less in each case than one molecular equivalent for each cyanogen group contained in the gas in the form of dicyanogen or hydrocyanic acid.

3. A process for the removal of cyanogen compounds from gases comprising bringing gasesat a temperature above 30 C. and containing cyanogen compounds into contact with an ammonium polysulphide liquor containing ammonium polysulphides higher than bisulphides to remove the cyanogen compounds from said gases and maintaining a' sufiicient excess of the said -higher polysulphidesin the liquor throughout the washing process to prevent the formation of ammonium monosulphides; excess of higher polysulphidesbeing maintained in the liquor by adding thereto during the washing process a quantity of sulphur and ammonia not less in each case than one molecular equivalent foreach cyanogen group contained in the gas in the form of dicyanogen or hydrocyanic acid.

CHRISTIAN JOHANNES HANSEN. 

